Embolizing sclerosing hydrogel

ABSTRACT

A sclerosing embolizing hydrogel comprising from about 0.1% by weight to about 4.0% by weight of chitosan; from about 0.01M to about 1M of hydrochloric acid; from 0% by volume to about 40% by volume of iopamidol; from 0.5% by weight to about 25% by weight of β-glycerophosphate disodium salt; and from about 0.05% by weight to about 4% by weight of sodium tetradecyl sulphate. Also a kit for synthesizing the hydrogel and a method using the hydrogel to treat a vascular defect in a subject.

The present application claims priority from U.S. Provisional patentapplication Ser. No. 61/344,089 filed May 20, 2010, the contents ofwhich is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the art of medical treatments. Morespecifically, the present invention is concerned with an embolizingsclerosing hydrogel and its applications in treatments of vasculardefects.

BACKGROUND

Endovascular aneurysm repair is an alternative to surgical repair ofabdominal aortic aneurysm which enables to reduce patient operatingrisks and time of recovery. However, this treatment is presently limitedby the persistence of blood leaks (called endoleaks). Some of theseendoleaks (type II endoleaks) can be treated by injecting an embolizingagent to block blood flow.

Several embolizing agents (mainly N-butyl-2-cyanoacrylate (NBCA) [1-4],Ethylenevinyl alcohol copolymer (EVOH, Onyx® [5, 6], polyurethanefragments and fibrin glue [7], combined or not with coils [4, 8]) havebeen tested recently for the treatment of endoleaks or for theirprophylactic prevention by injection into the aneurismal sac. Althoughthese studies showed that sac embolization has potential to minimizeendoleak occurrence, they also show that materials existing presentlyare limited. Recurrence of endoleaks are frequent. It is believed to bedue to recanalisation process through or around the injected materials.The same limitation occurs when prophylactic injection of embolizingagent around the implant is performed in order to prevent endoleakformation [3, 9, 10]. It is believed that combining embolizing andsclerosing properties would improve clinical results by inducingendothelial denudation and thus preventing recanalisation processes andpromoting fibrosis and healing. The only commercialized embolizing agentthat may present sclerosing properties to date is cyanoacrylate. Howeverthis agent is not biodegradable and such embolizing agent do not existpresently or they do not present adequate mechanical and biodegradationproperties.

In the case of arteriovenous malformation, sclerosing agents such asethanol and sodium tetradecyl sulphate foams are already used topermanently occlude the vessels. However, these agents are far fromideal since their poor mechanical properties make injection difficult tocontrol and do not enable to efficiently occlude blood flow.

Endovascular aneurysms repair (EVAR) clinical outcome is severelylimited by the persistence of blood flow perfusing the aneurysm, calledendoleaks, observed in 10% to 36% of cases [14-17]. The most frequenttype of endoleak is type II endoleak, which corresponds to retrogradeflow from collateral arteries [18, 19]. Persistent type II endoleakswith sac size progression require interventions as they can lead toaneurysm rupture [14, 15, 17, 18, 20-26]. Several attempts have beenrecently made to treat or prevent type II endoleaks using coils orpolymeric embolising agents (mainly N-butyl-2-cyanoacrylate (NBCA)[1-4], Ethylenevinyl alcohol copolymer (EVOH, Onyx® [5, 6], polyurethanefragments [27] and fibrin glue [7], combined or not with coils [4, 8].These studies showed that sac embolization has potential to minimizeendoleak occurrence. However, embolization failure (recurrence,recanalisation) was reported with all tested agents. Prophylacticembolization of the inferior mesenteric and/or lumbar arteries or of theentire aneurismal sac during EVAR has also been proposed in patients toprevent endoleak formation, once again with limited success [3, 9, 10].Uflacker et al. reported a high proportion of residual leaks in ananimal model despite deacetylated glucosamine injection into theaneurysm [28]. In a human study, injection of fibrin glue decreased therate but did not completely prevent type II endoleaks (2.4%) [7].Injectable agents developed to date are not only unable to treat orprevent all endoleaks. They are also far from ideal for such clinicaluse. Cyanoacrylate and Onyx are difficult to control during injection,are non-biodegradable and non porous, thus preventing tissue healing inthe cast. Their long-term biocompatibility is questionable. Moreoverthey are also very radiopaque and could create a diagnostic challenge insurveillance imaging studies. The two components of fibrin glue must beinjected separately and cannot easily fill up the cavity, since theyimmediately form a blood clot.

Accordingly, there is a need in the industry to provide a gel forrepairing aneurysms and other vascular defects. An object of the presentinvention is therefore to provide such a gel.

SUMMARY OF THE INVENTION

In a broad aspect, the invention provides a sclerosing embolizinghydrogel comprising: from about 0.1% by weight to about 4.0% by weightof chitosan; from about 0.01M to about 1M of an acid; from 0.5% byweight to about 25% by weight of β-glycerophosphate disodium salt; andfrom about 0.05% by weight to about 4% by weight of sodium tetradecylsulphate.

In some embodiments of the invention, the acid is selected from thegroup consisting of: acetic acid, ascorbic acid, salicylic acid,phosphoric acid, hydrochloric acid, propionic acid, formic acid, lacticacid and mixtures thereof. In a very specific embodiment of theinvention, the acid is hydrochloric acid.

In some embodiments of the invention, the hydrogel has a pH of fromabout 7 to about 7.4. This pH is physiological and advantageous forinjection in the human body.

In some embodiments of the invention, the hydrogel further comprises animaging contrast agent. For the purpose of this document an imagingcontrast agent is a substance that improves the visibility of thehydrogel when using a medical imaging device when compared to asituation in which the contrast agent is not present in the hydrogel.For example, the imaging contrast agent is a radiopaque substance, butother types of contrast agent are within the scope of the presentinvention. For example, the imaging contrast agent is a radiopaquesubstance. In some embodiments of the invention, the imaging contrastagent is selected from the group consisting of: Hypaque Meglumine, Reno,Conray, Renograffin, Hypaque Sodium, Hexabrix, Oxilan, iohexol(Omnipaque), iopamidol (Isovue), iopromide (Ultravist), ioversol(Optiray), iodixanol (Visipaque), iothalamate (Conray) and ioxaglate(Hexabrix). Iohexol (Omnipaque), iopamidol (Isovue), iopromide(Ultravist) and ioversol (Optiray) are non-ionic monomers. Iodixanol(Visipaque) is a non-ionic dimer. Iothalamate (Conray) is an ionicmonomer. Ioxaglate (Hexabrix) is an ionic dimer. The proposed hydrogelis therefore usable with a wide range of divers imaging contrast agents.

In a specific embodiments of the invention, the imaging contrast agentis iopamidol. For example, the hydrogel comprises from 0% by volume toabout 40% by volume of iopamidol.

In some embodiments of the invention, the hydrogel has a storage modulusof from about 1 kPa to about 10 kPa. This storage modulus is as measuredwhen the hydrogel is completely gelled. Hydrogels having theseproperties are useful in many medical applications.

In some embodiments of the invention, the chitosan has a degree ofdeacetylation of from about 80% to about 95%. In some specificembodiments of the invention, the chitosan has a degree of deacetylationof from about 80% to about 85%. This percentage has been found to beoptimal for biodegradation of the hydrogel for certain procedures.Indeed, adjusting suitably the degree of deacetylation allows for anadjustment of the biodegradability of the hydrogel, and thereforeinfluences its rate of disappearance in the body.

In some embodiments of the invention, the hydrogel includes from about1% by weight to about 3% by weight of sodium tetradecyl sulphate. Whilethis interval is strictly supported by experimental data presentedhereinbelow, the larger interval for the concentration of STS givenhereinabove is thought to be achievable with useful mechanicalproperties in view of the experiments that were performed.

In a specific embodiment of the invention, the hydrogel includes about2% by weight of chitosan; about 0.1M of hydrochloric acid; about 12% byweight of β-glycerophosphate disodium salt; about 1% by weight of sodiumtetradecyl sulphate; and about 20% by volume of iopamidol.

In another specific embodiment of the invention, the hydrogel includes:about 2% by weight of chitosan; about 0.1M of hydrochloric acid; about10% by weight of β-glycerophosphate disodium salt; about 3% by weight ofsodium tetradecyl sulphate; and about 20% by volume of iopamidol.

In another broad aspect, the invention provides a kit for synthesizing asclerosing embolizing hydrogel, the kit comprising: a first containercontaining chitosan in an acid solution; and a second containercontaining β-glycerophosphate disodium salt and sodium tetradecylsulphate.

In some embodiments of the invention, the first container also containsan imaging contrast agent. In some embodiments of the invention, the kitfurther comprises a mixer for mixing the contents of the first andsecond containers. In some embodiments, the second container contains anaqueous solution in which β-glycerophosphate disodium salt and sodiumtetradecyl sulphate are dissolved. In other embodiments, theβ-glycerophosphate disodium salt and sodium tetradecyl sulphate areprovided in any other suitable manner.

In another broad aspect, the invention provides a method for treating avascular defect in a subject, for example a non-human mammal or a human,the method comprising implanting at an implantation site in the subjectthe hydrogel as defined hereinabove. For the purpose of this document,the terminology vascular defect relates to a vascular structure thatrequires an alteration.

In some embodiments of the invention, the vascular defect is selectedfrom the group consisting of: an aneurysm, an abdominal aortic aneurysmand a vascular anomaly. In some examples, the vascular defect is anendoleak after endovascular aneurysm repair. In other examples, thevascular defect is a vascular anomaly selected from the group consistingof an arteriovenous malformation, a venous malformation, a lymphaticmalformation, an hemangioma, a varicocele and pelvic congestionsyndrome.

In some embodiments of the invention, the implantation site issubstantially adjacent the vascular defect.

In some embodiments of the invention, the method uses a catheterdefining a catheter proximal end and an opposed catheter distal end.Implanting the hydrogel includes: inserting the catheter in the subjectwith the catheter distal end positioned substantially adjacent theimplantation site and the catheter proximal end provided outside of thesubject; mixing precursor solutions of the hydrogel outside of thecatheter to form a mixed hydrogel forming solution and injecting thehydrogel forming solution through the catheter at the implantation site.The hydrogel is thus implanted at the implantation site. For the purposeof this document, the terminology hydrogel forming indicates a solutionthat is in process of gelation or which has completed this process.

In some embodiments of the invention, the method further includesstenting the vascular defect before injecting the hydrogel formingsolution. In some embodiments of the invention, the method furtherincludes excluding blood flow at the implantation site before injectingthe hydrogel forming solution.

The present invention relates to a new injectable embolizing materialwith sclerosing properties. While many uses for the hydrogel have beendescribed hereinabove, such material could also be used to treat otherpathologies, such as for the treatment of cancer.

Many pathologies require embolizing treatments but materials existingpresently do not lead to satisfactory results. The proposed hydrogel isa new embolizing material based on a new paradigm and which has uniqueproperties enabling a safe, efficient and durable embolization.

The terminology “about” as used in this document qualifying a quantityrefers to small variations in the numerical value qualified that wouldnot affect the physical and chemical properties of the proposed hydrogelin a significant manner, as appreciated by a person skilled in the art.

The present application cites many documents, the contents of which ishereby incorporated by reference in their entirety.

Other objects, advantages and features of the present invention willbecome more apparent upon reading of the following non-restrictivedescription of preferred embodiments thereof, given by way of exampleonly with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, in an X-Y graph illustrates the time dependence of storagemodulus (G′) of a radiopaque hydrogel in accordance with an embodimentof the invention as a function of sodium tetradecyl sulphate (STS)concentration (0, 1, 2 and 3% w/v) at 37° C., increasing concentrationsof STS providing an improvement in rheological and mechanical propertiesfor embolization;

FIG. 2, in an X-Y graph, illustrates the time dependence of storage (G′)and loss (G″) moduli of a radiopaque STS solution (20% v/v iopamidol(IOP), 3% w/v STS, without chitosan hydrogel) at 37° C., a viscousliquid behavior being observed without any rigid mechanical properties;

FIG. 3, in a bar chart, illustrates the storage modulus (G′) ofradiopaque chitosan hydrogel (2% w/v chitosan (CH), 20% v/v IOP, 12% w/vβ-glycerophosphate (βGP) obtained after 1 week of gelation at 37° C. asa function of STS concentration (0, 1, 2 and 3% w/v), showing that thestorage modulus is increased after 1 week as a function of STSconcentration, thus enabling better embolization properties, the presentinvention solving many problems inherent in the art as the chitosan/STShydrogel is much stronger than the STS (3%) foam and can displace theblood into aneurysm more effectively;

FIG. 4, in a photograph, illustrates the porous structure of thechitosan/STS hydrogel (2% w/v CH, 20% v/v IOP, 12% w/v βGP, 3% w/v STS),as observed by scanning electron microscopy after gold sputtering;

FIG. 5, in an X-Y graph, illustrates the swelling properties as afunction of STS concentrations (2% w/v CH, 12% w/v βGP, 20% v/v IOP) ofchitosan hydrogel immersed in PBS buffer at 37° C., where an * indicatesa significant differences (p<0.05) of swelling equilibrium obtainedafter 8 days compared to chitosan hydrogel; and

FIG. 6, in a flowchart, illustrates a method for treating a vasculardefect in a subject in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

The present invention relates to the development of an embolizing agentwith sclerosis properties which combines appropriate mechanical,biocompatibility, biodegradation and gelation properties for suchapplications. The hydrogel created is based on chitosan, a biocompatiblebiodegradable biomaterial and sodium tetradecyl sulphate (STS), asclerosing agent. Methods were developed to create an embolic sclerosinghydrogel which does not precipitate, has superior mechanical propertiesand enables controlled injection.

The present invention relates to an embolic hydrogel with sclerosingproperties. The composition of this hydrogel is:

-   -   Chitosan (CH).    -   β-glycerophosphate (βGP).        -   Sodium tetradecyl sulphate (STS).    -   Depending on the desired application, the hydrogel can be        created radiopaque or not, by addition of a contrast agent such        as Iopamidol (or others). Radiopacity is important in some        treatments of abdominal aortic aneurysms. It is sometimes not        required for some vascular malformations. Also, it is        contemplated to use other imaging contrast agents for augmenting        the contrast of the hydrogel using other imaging modalities.

The unique combination of chitosan, βGP and STS enables to create anembolic sclerosing hydrogel with good mechanical properties, that can beinjected easily and has immediate mechanical properties adequate forembolization, as illustrated in FIG. 1. The addition of a contrast agentsuch as Iopamidol does not prevent gelation and only slightly increasesits final mechanical properties.

The unique association of chitosan, βGP and STS provides moreappropriate rheological and mechanical properties compared tochitosan+βGP (FIG. 1) or to STS alone, which is liquid (FIG. 2). It isalso possible to create an hydrogel that has many properties suitablefor medical treatment, such as a physiological pH, for example between7.0 and 7.4.

The addition of β GP enables to add STS to chitosan without inducing itsprecipitation. The procedure of fabrication itself (pH of each componentbefore mixing and the order of addition) is important to avoidprecipitation or phase separation of chitosan at physiological pH, asshown in Table 1.

The proposed hydrogel is an elastic material (G′>1000 Pa), as comparedto STS foam (viscous material) that is presently used in the treatmentof arteriovenous malformations (FIG. 2).

The proposed hydrogel increases the storage modulus of chitosan+βGPhydrogels, thus enabling better embolization properties, as illustratedin Table 2. For example, just after mixing, G′ of chitosan+βGP is around10 Pa compared with chitosan/STS (1357 Pa). After 1 week of gelation at37° C., G′ of chitosan+βGP is 1213 Pa compared with chitosan/STS (3297Pa) (FIG. 3).

The proposed hydrogel adds sclerosing properties to chitosan, whichprevents recanalisation processes and promotes fibrosis (healing).

The hydrogel is a porous matrix appropriate for cell invasion duringhealing process, as shown in FIG. 4.

The hydrogel can be become radiopaque by addition of a non-ioniccontrast agent (for example at 20% v/v) which does not significantlymodify its gelation or mechanical properties. The contrast agent issimply entrapped in the hydrogel and is rapidly eliminated and thus doesnot to interfere with further imaging follow-up.

If required, the two solutions required to create the chitosan/STShydrogel can be sterilized before mixing and the chitosan/STS hydrogelis considered as a ready-to-use biomaterial. Indeed, the proposedhydrogel can be provided as a kit in which a first container a firstcontainer contains chitosan in an acid solution and a second containercontaining β-glycerophosphate disodium salt and sodium tetradecylsulphate. In some embodiments, the first container also contains animaging contrast agent. The containers contain sufficient quantities ofmaterials at proper concentrations to synthesize an hydrogel for theapplication for which it is intended in sufficient quantity.

The two solutions used to create the hydrogel can be mixed in theoperating room, using a suitable mixer, and then injected via catheterwithout significant damage on its mechanical properties.

The proposed hydrogel is believed to be the first product withsclerosing properties proposed to treat endoleaks or do prophylacticprevention of endoleaks in abdominal aortic aneurysms. The two principleroles of the chitosan/STS hydrogel are the embolization of aneurysm sacsor other structures (to block any blood flow entering the aneurysms) andto cause an irreversible endothelial injury in the aneurysm sac (orother structure) to prevent recanalisation process by endothelial cellsthat could lead to recurrence of blood flow after a while, this processbeing thought to be a cause of failure of presently used embolictreatments.

Such an embolic sclerotic agent has a large commercial potential for thetreatment of endoleak or for their prophylatic prevention by injectionjust after stent-graft (SG) deployment. The proposed hydrogel has manyadvantages compared to presently used agents (mainly Histoacryl(cyanoacrylate) and Onyx (polyvinyalcool mixed with dimethyl sulfoxide(DMS), Embogel (Alginate mixed with calcium chloride). Indeed:

1) The hydrogel's sclerosing effect is well controlled. STS is ananionic surfactant that has been demonstrated to destroy endotheliallining in vivo. It is commonly used in sclerotherapy. Its combinationwith the cationic chitosan limits its diffusion during the EVARprocedure and thus decreases safety risks. It can be added at anyconcentrations, based on clinical data). In Onyx, DMSO can also have asclerosing effect. Yet DMSO is liquid and can be easily release insurrounding tissues.

2) Gelation of chitosan/STS was found to be adequate to allow easyclinical handling, positioning and injection while limiting risks ofmigration in vivo. The rapid increase of storage modulus avoids risks ofmigration but does not require to be mixed in vivo as other products,nor create risk of catheter adhesion in vivo. In contrast, rapidpolymerisation of cyanoacrylate can lead to catheter obstruction andsticking into the treated arteries.

3) The mechanical properties of the proposed hydrogel (above 1000 Paafter gelation) are sufficient for flow occlusion in the aneurismal sacbut its viscosity allows it to easily fill and mold to any shape ordefect in vivo (in contrast to cyanacrylate that often lead to emptyspaces).

4) Chitosan is biocompatible and biodegradable. It forms a porous matrixwhich can be infiltrated and progressively replaced by tissue, thus notimpairing the healing process after EVAR [11] in contrast to permanentOnyx and cyanoacrylate that are permanent.

5) Chitosan/STS is also biodegradable. After injection in the rabbitauricular artery, chitosan/STS prepared with chitosan 83% DDA was shownto be replaced by fibrous tissue within 1 month. The degree ofdeacetylation (DDA) of chitosan can be modified to modify thedegradation rate.

6) Chitosan is hemostatic and may thus favour thrombosis in theaneurismal sac [11]. It is muco-adhesive, and by binding withsurrounding tissues, should allow good flow occlusion and limitmigration.

The addition of β-glycerophosphate salt allows to avoid precipitation ofchitosan before its gelation in a viscoelastic hydrogel. Addition ofsodium tetradecyl sulphate increases the gelation rate and leads tobetter mechanical properties compared to chitosan alone, ascharacterized by rheometry (FIG. 3). This allows good embolizationproperties in vivo, as assessed on efficient embolization of renalartery, as described hereinbelow.

Example

Materials & Methods

Materials

Medium molecular weight (Mw) chitosan (Mw˜4.2×10⁵ Da) with a relativelyhigh degree of deacetylation (DDA˜83%) and β-glycerophosphate disodiumsalt hydrate (βGP) were used in this study. Chitosan with other DDAcould be used alternatively to modify the degradation rate. The imagingcontrast agent used in this study was iopamidol (IOP) from BraccoDiagnostics Inc. (Canada) but other liquid iodinated contrast agents canalso be used. Also, in other embodiments of the invention, othersuitable imaging contrast agents are usable. Sodium tetradecyl sulphate(STS), dibasic sodium phosphate, monobasic sodium phosphate andhydrochloric acid were acquired from Sigma-Aldrich (Canada).

Preparation of STS Solution at Physiological pH

Different STS solutions were prepared at different concentrations bydiluting STS solution (27% w/v) until an appropriate volume of dibasicsodium phosphate/monobasic sodium phosphate was obtained.

Preparation of Radiopaque Chitosan Hydrogel with Sclerosing Properties:Chitosan/STS

A chitosan solution was prepared by dissolving chitosan powder in 0.1MHCl with an appropriate amount of iopamidol at room temperature underconstant magnetic stirring. The sample was sterilized at 121° C. for 20min and stoked at 4° C. for 24 h. βGP-STS solutions were prepared bydissolving an appropriate amount of βGP powder in STS solution. TheβGP-STS solution was then sterilized using a 0.2 μm filter. The βGP/STSsolution was mixed with chitosan solution to form the radiopaquechitosan hydrogel at 37° C. with sclerosing properties (chitosan/STS).

Rheological Measurements

Rheological measurements were performed using the Bohlin CVO rheometre(Malvern Instruments Inc., USA) equipped with co-axial cylinder orparallel-plate geometry and a circulating water bath to control thetemperature. Rheological data were collected using the Bohlin software.Small-amplitude oscillatory shear experiments were performed at 37° C.The time evolution of storage (or elastic) modulus G′ and loss (orviscous) modulus G″ was determined within the linear viscoelasticregion, at fixed frequency (1 Hz) and stress amplitude (1 Pa). The timedependence of G′ and G″ of chitosan hydrogels were measured as afunction of STS concentration. The gelation time (t_(gel)) was thendetermined as the time at which G′=G″ in accordance with the approachproposed in the literature [12, 13]. The study was performed intriplicate.

Swelling Properties

After the hydrogel reached gelation equilibrium (1 week of gelation at37° C.), the degree of swelling was determined by keeping lyophilizedspecimens in phosphate buffer solution (pH 7.4) at 37° C. and recordingvariations in their weight in comparison to their initial weight (W₀).At regular time intervals, the hydrogels were weighed (W_(t)) and mediumwas changed. The swelling ratio (S_(w)) of hydrogels was calculatedusing the following equation:

$S_{w} = \frac{W_{t} - W_{0}}{W_{0}}$where W_(t) and W₀ are the weights of the water-swollen samples and theinitial lyophilized hydrogel samples, respectively. The study wasperformed in triplicate. Results are shown in FIG. 5.

Morphology of Chitosan/STS Hydrogels

The morphology of chitosan/STS hydrogels was observed by scanningelectron microscopy (SEM). After 1 week of gelation at 37° C., theprepared specimens were freeze-dried under vacuum during 24 h andsputter-coated with gold, and their morphology was observed. As chitosanhydrogels, chitosan-STS hydrogels were shown to exhibit a porousstructure, as seen in FIG. 4.

In Vivo Testing of Chitosan/STS Hydrogels

Chitosan/STS hydrogels were tested in vivo in various studies.

-   -   Rabbit artery model: The objective of this experiment was to        investigate if embolization with chitosan/STS can prevent        endothelial recanalization in a rabbit auricular artery (AA)        model. Each AA was canulated and injected with 0.6 ml of        chitosan (chitosan 2% w/v, iopamidol 20% v/v, BGP 12% w/v) (OCh;        n=14) on one side and either saline (OSal; n=2), chitosan/STS 1%        (chitosan 2% w/v, iopamidol 20% v/v, BGP 12% w/v, STS 1% w/v)        (OCS1; n=6), or chitosan/STS 3% (chitosan 2% w/v, iopamidol 20%        v/v, BGP 12% w/v, STS 3% w/v) (OCS3; n=6) in the controlateral        side (randomly assigned). All hydrogels were prepared and        sterilized as described hereinabove. AA patency and percentage        of recanalisation was assessed by visual inspection and Laser        Doppler after embolization and at 1, 7, 14, and 30 days. The        rabbits were sacrificed at 30 days to assessed endothelial        ablation and inflammatory response by histological analyses. All        AA's were catheterized and embolized with success. After 30        days, all the OSal were patent. Percentage of recanalization in        comparison with initial embolization length were 25.6+/−34.4% in        OCS1 (6+/−7 mm), and 22.5+/−15.9% in OCS3 (12+/−8 mm) without        statistical difference with student test (p 0.05). At histology,        chitosan/STS was shown to generate inflammatory response and was        then replaced by fibrous tissue.    -   Canine model of aneurysms reproducing endoleaks after        endovascular aneurysm repair with a stent-graft were created in        3 dogs. One endoleak was treated by chitosan/STS (chitosan 2%        w/v, iopamidol 20% v/v, BGP 12% w/v, STS 3% w/v) and its        controlateral control by chitosan (chitosan 2% w/v, iopamidol        20% v/v, BGP 12% w/v). All hydrogels were prepared and        sterilized as described hereinabove. Chitosan/STS led to good        control during embolization while chitosan hydrogel showed some        migration into the collaterals. No migration into the        stent-graft lumen was observed. One small leak was visible by        angiography just after embolization but disappeared during the        first week. At three months, no endoleak was detected while        endoleak was present in ⅓ aneurysm treated with chitosan alone.        In this challenging animal model, untreated endoleak persist in        all aneurysms when left untreated.

While only some examples of hydrogels in accordance with the inventionare provided, it is believed that a hydrogel according to the claimswill have similar beneficial properties. Notably, it is believed, fromthe common knowledge present in the field of the invention and theexperimental data obtained, that the following composition for thehydrogel would produce a useful hydrogel:from about 0.1% by weight toabout 4.0% by weight of chitosan; from about 0.01M to about 1M of anacid; from 0.5% by weight to about 25% by weight of β-glycerophosphatedisodium salt; and from about 0.05% by weight to about 4% by weight ofsodium tetradecyl sulphate. Notably, while hydrochloric acid was used inthis example, it is believed that at least for some applications forwhich the gel is intended, other acids such as acetic acid, ascorbicacid, salicylic acid, phosphoric acid, propionic acid, formic acid,lactic acid and mixtures thereof are usable.

The above suggest an embolization procedure to treat aneurisms, othervascular defects and other pathologies and defects. The procedure isexemplified by the method 100 shown in FIG. 6. The embolizationprocedure is similar to that of other polymeric embolization agents suchas Onyx and Histoacryl. For the prevention of endoleaks after EVAR, theagent could be easily injected at the time of the endovascular treatmentby an angiographic catheter which would be placed into the aneurysmbefore stent-graft deployment. Once the stent-graft is deployed, theaneurysm is excluded from blood flow and the agent can be safelyinjected into the aneurysmal sac.

To minimize risks of migration in collateral vessel, an occlusiveballoon catheter can be deployed proximally in the vessel to avoid bloodflow. The volume of the agent to be injected could be evaluated beforebased on imaging data. Injection through a Glicath 4 French (Terumo,Tokyo, Japan) have been tested with success both in vitro and in vivo.

When an endoleak has been observed during stent-graft imaging follow-up,the agent can be used to treat the endoleak. In this case, the agentcould be injected by a microcatheter (for example a 3 French catheter)positioned in the collateral vessel involved in the leak. It could alsobe injected by direct punction into the aneurysm (under CT scan orfluoroscopy). In this case, the agent is injected with a needle (forexample 21 or 22 gage) then replaced by a micropunction system and acatheter or microcatheter. In this circumstances, only a small volumewould be injected into the endoleak area.

For arteriovenous malformations or other treatments, the agent can beinjected directly in the nidus by a needle, or using a catheter whennecessary.

The proposed hydrogel is also usable in many other treatments, forexample to treat varicose veins and cancer, the later, for example, byserving as a vehicle for a therapeutic agent. In addition, STS can acton blood irrigation of a tumor though its sclerosing properties, as wellas acting on the tumor through these same properties. In theseapplications, the proposed hydrogel is used in replacement to hydrogelsused in similar methods in the prior art.

More generally, the method 100 starts at step 105. The method uses acatheter defining a catheter proximal end and an opposed catheter distalend. At step 110, the catheter is inserted in a subject to treat withthe catheter distal end positioned substantially adjacent animplantation site and the catheter proximal end provided outside of thesubject.

Then, at step 115, precursor solutions of the hydrogel are mixed outsideof the catheter to form a mixed hydrogel forming solution. An hydrogelforming solution is a solution in process of gelation, gelation can bepartial or total prior to implantation in the subject, depending on thespecific application contemplated. The precursor solutions includes thecomponents of the hydrogel. For example, one of the precursor solutionincludes chitosan dissolved in HCl, and a second precursor solutionincludes βGP and STS.

At step 130 the hydrogel forming solution is injected through thecatheter at the implantation site and the hydrogel is implanted at theimplantation site, where gelation continues, if necessary. The methodends at step 135

In some embodiments, the method includes a step 120 of stenting thevascular defect before injecting the hydrogel forming solution. In someembodiments, the method also includes a step 125 of excluding blood flowat the implantation site before injecting said hydrogel formingsolution, using conventional methods.

The order of some of the above-recited steps can be changed withoutdeparting from the scope of the invention, as the reader skilled in theart will readily appreciate.

Although the present invention has been described hereinabove by way ofpreferred embodiments thereof, it can be modified, without departingfrom the spirit and nature of the subject invention as defined in theappended claims.

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TABLE 1 Order of preparation to obtain a chitosan hydrogel withsclerosing properties at physiological pH. Hydrogel Order of preparationformation Remarks CH + STS N Precipitation and phase separation ofchitosan solution. [CH + STS] + βGP N Precipitation and phase separationof chitosan solution. The βGP addition didn't improve the hydrogelformation. [CH + βGP] + STS N Phase separation of chitosan solution.CH + βGP Y Homogenous and injectable hydrogel without sclerosingproperties. CH + [βGP + STS] Y Homogenous and injectable hydrogel withsclerosing properties.

TABLE 2 Influence of STS concentration on rheological characteristics ofchitosan hydrogel at 37° C. (2% w/v CH, 20% v/v IOP, 12% w/v βGP). STS(% pH at Formulation w/v) 23° C. t_(gel) (min) G′₀ (Pa)* G′_(∞) (Pa)+CH/βGP-STS-0 0 7.24 897 ± 121 10 ± 1 1213 ± 79  CH/βGP-STS-1 1 7.30Immediate  40 ± 23 1716 ± 402 CH/βGP-STS-2 2 7.34 Immediate 444 ± 212724 ± 275 CH/βGP-STS-3 3 7.39 Immediate 1357 ± 387 3297 ± 351 *Initialstorage modulus at time 0. +Storage modulus after one week of gelation.

We claim:
 1. A sclerosing embolizing hydrogel comprising: from about0.1% by weight to about 4.0% by weight of chitosan; from about 0.01M toabout 1M of an acid; from 0.5% by weight to about 25% by weight ofβ-glycerophosphate disodium salt; and from about 0.05% by weight toabout 4% by weight of sodium tetradecyl sulphate.
 2. The hydrogel asdefined in claim 1, wherein said acid is selected from the groupconsisting of: acetic acid, ascorbic acid, salicylic acid, phosphoricacid, hydrochloric acid, propionic acid, formic acid, lactic acid andmixtures thereof.
 3. The hydrogel as defined in claim 1, wherein saidacid is hydrochloric acid.
 4. The hydrogel as defined in claim 1,wherein said hydrogel has a pH of from about 7 to about 7.4.
 5. Thehydrogel as defined in claim 1, further comprising an imaging contrastagent.
 6. The hydrogel as defined in claim 5, wherein said imagingcontrast agent is a radiopaque substance.
 7. The hydrogel as defined inclaim 5, wherein said imaging contrast agent is selected from the groupconsisting of: Hypaque Meglumine, Reno, Conray, Renograffin, HypaqueSodium, Hexabrix, Oxilan, iohexol (Omnipaque), iopamidol (Isovue),iopromide (Ultravist), ioversol (Optiray), iodixanol (Visipaque),iothalamate (Conray) and ioxaglate (Hexabrix).
 8. The hydrogel asdefined in claim 7, wherein said imaging contrast agent is iopamidol. 9.The hydrogel as defined in claim 8, wherein said hydrogel comprises from0% by volume to about 40% by volume of said iopamidol.
 10. The hydrogelas defined in claim 1, wherein said hydrogel has a storage modulus offrom about 1 kPa to about 10 kPa.
 11. The hydrogel as defined in claim1, wherein said chitosan has a degree of deacetylation of from about 80%to about 95%.
 12. The hydrogel as defined in claim 1, wherein saidchitosan has a degree of deacetylation of from about 80% to about 85%.13. The hydrogel as defined in claim 1, wherein said hydrogel includesfrom about 1% by weight to about 3% by weight of sodium tetradecylsulphate.
 14. The hydrogel as defined in claim 1, wherein said hydrogelincludes: about 2% by weight of chitosan; about 0.1M of hydrochloricacid; about 12% by weight of β-glycerophosphate disodium salt; and about1% by weight of sodium tetradecyl sulphate; and wherein said hydrogelfurther comprises about 20% by volume of iopamidol.
 15. The hydrogel asdefined in claim 1, wherein said hydrogel includes: about 2% by weightof chitosan; about 0.1M of hydrochloric acid; about 10% by weight ofβ-glycerophosphate disodium salt; and about 3% by weight of sodiumtetradecyl sulphate; and wherein said hydrogel further comprises about20% by volume of iopamidol.
 16. A method for treating a vascular defectin a subject, said method comprising implanting at an implantation sitein said subject the hydrogel as defined in claim
 1. 17. The method asdefined in claim 16 wherein said vascular defect is selected from thegroup consisting of: an aneurysm, an abdominal aortic aneurysm and avascular anomaly.
 18. The method as defined in claim 16, wherein saidvascular defect is an endoleak after endovascular aneurysm repair. 19.The method as defined in claim 16, wherein said vascular defect is avascular anomaly selected from the group consisting of an arteriovenousmalformation, a venous malformation, a lymphatic malformation, anhemangioma, a varicocele and pelvic congestion syndrome.
 20. The methodas defined in claim 16, wherein said implantation site is substantiallyadjacent said vascular defect.
 21. The method as defined in claim 16,said method using a catheter defining a catheter proximal end and anopposed catheter distal end, wherein implanting said hydrogel includes:inserting said catheter in said subject with said catheter distal endpositioned substantially adjacent said implantation site and saidcatheter proximal end provided outside of said subject; mixing precursorsolutions of said hydrogel outside of said catheter to form a mixedhydrogel forming solution; injecting said hydrogel forming solutionthrough said catheter at said implantation site; whereby said hydrogelis implanted at said implantation site.
 22. The method as defined inclaim 21, further comprising stenting said vascular defect beforeinjecting said hydrogel forming solution.
 23. The method as defined inclaim 21, further comprising excluding blood flow at said implantationsite before injecting said hydrogel forming solution.
 24. The method asdefined in claim 16, wherein said subject is a non-human mammal.
 25. Themethod as defined in claim 16, wherein said subject is a human.